High-frequency oscillator

Abstract

A frequency-selective high-frequency oscillator includes a first switching circuit that controls the operation of a first amplifying circuit, and a second switching circuit that controls the operation of the first switching circuit and a second amplifying circuit. Switching control signals are input to the second switching circuit. When the switching control signal is “Low”, the second switching circuit turns ON and the second amplifying circuit only operates, thereby outputting a high frequency signal with a resonant frequency according to a second resonant circuit. On the other hand, when the switching control signal is “High”, the second switching circuit turns OFF and the first switching circuit turns ON, which causes the first amplifying circuit only to operate. Thus, a high frequency signal with a resonant frequency acceding to a first resonant circuit is output.

1. A high frequency oscillator comprising:
 a first resonant circuit and a second resonant circuit which oscillate at different resonant frequencies from each other; 
 a first amplifying circuit including an NPN transistor, the first amplifying circuit being connected to the first resonant circuit; 
 a second amplifying circuit including an NPN transistor, the second amplifying circuit being connected to the second resonant circuit; 
 a buffer circuit arranged to amplify a signal input from one of the first amplifying circuit and the second amplifying circuit; and 
 a selection circuit arranged to switch operation between the first amplifying circuit and the second amplifying circuit; wherein 
 the selection circuit includes: 
 a first switching circuit including a PNP transistor having a collector terminal connected to a base terminal of the NPN transistor of the first amplifying circuit and an emitter terminal connected to a power supply; 
 a second switching circuit including a PNP transistor having a collector terminal connected to a base terminal of the NPN transistor of the second amplifying circuit and an emitter terminal connected to the power supply; and 
 only one switching control signal input terminal for inputting a control signal; wherein 
 the base terminal of the PNP transistor of the second switching circuit is connected to the switching control signal input terminal and the collector terminal of the PNP transistor of the second switching circuit is connected to the base terminal of the PNP transistor of the first switching circuit. 
 
   
   
     2. The high frequency oscillator according to  claim 1 , wherein a third switching circuit is disposed between the switching control signal input terminal and the second switching circuit, the third switching circuit including an NPN transistor having a collector terminal connected to the base terminal of the PNP transistor of the second switching circuit, a grounded emitter terminal, and a base terminal connected to the switching control signal input terminal. 
   
   
     3. The high frequency oscillator according to  claim 1 , wherein at least the first switching circuit includes a PNP transistor. 
   
   
     4. The high frequency oscillator according to  claim 3 , wherein the first switching circuit includes a plurality of resistors. 
   
   
     5. The high frequency oscillator according to  claim 1 , wherein at least the second switching circuit includes a PNP transistor. 
   
   
     6. The high frequency oscillator according to  claim 5 , wherein the second switching circuit includes a plurality of resistors. 
   
   
     7. The high frequency oscillator according to  claim 1 , wherein at least two of amplifying circuits are connected to the first and second resonant circuits. 
   
   
     8. The high frequency oscillator according to  claim 7 , wherein at least two of the buffer circuits are provided and arranged to amplify signals input from the at least two amplifying circuits. 
   
   
     9. The high frequency oscillator according to  claim 1 , wherein the first switching circuit includes of a PNP transistor and the second switching circuit includes a PNP transistor and a resistor connected to a base terminal of the PNP transistor thereof. 
   
   
     10. The high frequency oscillator according to  claim 1 , wherein resistors are provided for supplying a bias current and the second switching circuit is connected between the resistors such that an emitter terminal of the PNP transistor is connected to one of the resistors and a collector terminal of the PNP transistor is connected to another of the resistors. 
   
   
     11. The high frequency oscillator according to  claim 2 , wherein the first switching circuit includes a PNP transistor, the second switching circuit includes a PNP transistor and a resistor connected between a base and an emitter of the PNP transistor thereof and a resistor connected to a base terminal of the PNP transistor thereof, and the third switching circuit includes a resistor connected to a base terminal of the NPN transistor thereof. 
   
   
     12. The high frequency oscillator according to  claim 2 , wherein a pair of resistors are provided and the first switching circuit includes a PNP transistor that is disposed between the pair of resistors. 
   
   
     13. The high frequency oscillator according to  claim 1 , wherein a pair of resistors are provided and the second switching circuit includes a PNP transistor that is disposed between the pair of resistors. 
   
   
     14. The high frequency oscillator according to  claim 1 , wherein two pairs of resistors are provided, the first switching circuit includes a PNP transistor that is disposed between the first pair of resistors and the second switching circuit includes a PNP transistor that is disposed between the second pair of resistors. 
   
   
     15. The high frequency oscillator according to  claim 1 , wherein the first switching circuit includes at least one resistor, and two additional resistors are provided, and one end of the resistor of the first switching circuit is connected between the two additional resistors. 
   
   
     16. The high frequency oscillator according to  claim 2 , wherein the buffer circuit includes an NPN transistor and series connected inductors are connected between a collector terminal of the NPN transistor of the buffer circuit and a power terminal, and a node between the inductors L 1  and L 2  is connected to a collector terminal of the NPN transistor of the third switching circuit.